BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a pneumatic cylinder and, more particularly, to
such a pneumatic cylinder which can prevent shocks that could damage its components
by reducing cushioning pressure, and can provide speedy working stroke by reducing
cushioning time.
Description of Related Art
[0002] Generally, the pneumatic cylinders convert fluid flowing under pressure to a linear
motion to perform mechanical work. One example of a conventional pneumatic cylinder
is illustrated in Figs. 1 and 2. The conventional pneumatic cylinder includes a cylinder
body defined by a barrel-like tube 102 and a pair of caps 104 and 106 fixedly disposed
on opposite ends of the tube 102, respectively.
[0003] The pneumatic cylinder further includes a piston rod 110 slidably extending through
the cap 106 into the inside of the tube 102 and a piston 108 fixed at the front end
of the rod 110 which is located in the tube 102. Each of the caps 104 and 106 is provided
with a plurality of fluid flow ports A and A' through which fluid can come in and
leave from the inside of the tube.
[0004] The cylinder further includes a cushioning device for preventing shocks caused by
reciprocating strokes of the piston 108. The cushioning device has a cushioning plunger
112 formed on the piston 108 and extending in a direction opposite to the rod 110,
and a cushioning ring 114 fitted around an extension 113 connecting the piston 108
and the rod 110 with each other.
[0005] Further, the inner surface of the cap 104 is provided with a passage 116 which communicates
with the port A and into which the plunger 112 can be slidably inserted. The inner
surface of the cap 106 is also provided with a passage 118 which communicates with
the port A' and into which the cushioning ring 114 can be slidably inserted Accordingly,
fluid within the cushioning chambers R and R' are to be returned to a fluid tank (not
shown) through each passage 116 and 118 in accordance with the movement of the piston
108.
[0006] When the passage 116(118) is closed by fitting the cushioning plunger 112(the cushioning
ring 114) thereinto in accordance with the movement of the piston, the fluid within
the cushioning chamber R(R') is not returned to the fluid tank any more through the
passage 116(118).
[0007] Accordingly, to provide a return passage for residual fluid, the caps 104 and 106
are respectively provided with orifices O and O' on their inner surfaces, which communicate
with the ports A and A', respectively.
[0008] Further, cushioning valves 120 and 122 are respectively provided on the caps 104
and 106 to restrict the fluid amount passing through the respective orifices O and
O' by regulating the opening thereof. This makes the cushioning of the piston which
depends on the returning velocity of the fluid be regulated.
[0009] In the cushioning device as described above, when the pressurized fluid comes into
the cushioning chamber R defined on the left side of the piston 108 through the port
and passage A and 116 of the cap 104, the piston 108 within tube 107 forces to the
right to perform the linear motion of the piston rod 110.
[0010] At this point, before the cushioning ring 114 formed on the extension of the piston
108 is inserted into the passage 118 of the cap 106 to close the passage 118, the
piston rapidly moves to the right as the fluid within the cushioning chamber C' defined
on the right side of the piston 108 returns to the fluid tank through the port and
passage A' and 118.
[0011] However, once the cushioning ring 114 closes the passage 118, the piston slowly moves
to the right as the residual fluid within the chamber C' returns to the fluid tank
through the port A' via the orifice O'. That is, by regulating elastic force and returning
velocity of the fluid, cushioning force applied to the piston 108 can be also regulated.
[0012] On the other hand, when the pressurized fluid comes into the cushioning chamber R


defined on the right side of the piston 108 through the port A' via the passage 118
of the cap 104, the piston 108 within tube 107 forces again to the left to accomplish
the reciprocating motion of the piston rod 110.
[0013] At this point, in a similar manner, before the cushioning plunger 112 formed integrally
on the left face of the piston 108 is inserted into the passage 116 of the cap 106
to close the passage 116, the piston rapidly moves to the left as the fluid within
the cushioning chamber C defined on the left side of the piston 108 returns to the
fluid tank through the port A via the passage 116.
[0014] However, once the cushioning plunger 112 obstructs the passage 116, the piston 108
slowly moves to the right as the residual fluid within the chamber C' returns to the
fluid tank through the passage A via the orifice O. That is, cushioning force which
is of elastic force of fluid generated by regulating its return velocity is applied
to the piston 108.
[0015] Fig. 11 is a graph for comparing a shock power change in response to cushioning operation
time and cushioning force of the piston 108 between the cushioning device of the present
invention and this conventional cushioning device, wherein the curve line X' shows
that the piston 108 receives cushioning force in a section Tss and the maximum shock
power Pps is 10kg f/cm
3.
[0016] On the one hand, the cushioning force applied to the piston 108 which reciprocates
in a state of receiving the shock power as described above can be regulated by the
cushioning valve which regulates opening the orifices O and O' for restricting fluid
flow amount.
[0017] However, since the pneumatic cylinder as described above suddenly restricts the returning
velocity of fluid, the shock applied to the cylinder increase such that the cylinder
has a short life. Additionally, since the cushioning operation time is getting longer,
the stroke time of the cylinder is retarded.
SUMMARY OF THE INVENTION
[0018] Accordingly, the objects of the present invention are to provide a pneumatic cylinder
which can prevent shocks that could damage its components by reducing cushioning pressure,
and can provide speedy working stroke by reducing cushioning time.
[0019] Additional objects and advantages of the invention will be set forth in part in the
description which follows, and in part will be obvious from the description, or may
be learned by practice of the invention. The objects and advantages of the invention
will be realized and attained by means of the elements and combinations particularly
pointed out in the appended claims.
[0020] To achieve the objects and in accordance with the purpose of the invention, as embodied
and broadly described herein, the invention provides a pneumatic cylinder comprising:
a cylindrical tube; first and second caps respectively fitted on opposite ends of
the cylinder tube, the first and second caps being provided with first and second
fluid flowing ports, respectively; first and second cushioning regulator valves respectively
mounted on the first and second caps to regulate cushioning force; a piston rod slidably
extending through one of the caps into the tube; a piston fixed at one end of the
piston rod 110 which is located in the cylindrical tube; and a cushioning device for
preventing shocks caused by the piston which reciprocates when fluid flows in or out
through the fluid flowing ports; wherein the cushioning device comprises a first cushioning
sleeve fixed on the piston and extending in a direction opposite to the piston rod,
the first cushioning sleeve gradually decreasingly communicating a first cushioning
chamber with a first passage formed on the first cap and connected to the first fluid
flowing ports as the first cushioning sleeve is gradually inserted into the first
passage; a second cushioning sleeve fixed around the one end of the piston rod, the
second cushion sleeve gradually decreasingly communicating a second cushioning chamber
with a second passage formed on the second caps and connected to the second fluid
flowing ports as the second cushioning sleeve is gradually inserted into the second
passage; a first quick fluid exhaust valve which is mounted on the first cap and is
selectively opened by pushing force of the piston to communicate the first cushioning
chamber with the first passage; a second quick fluid exhaust valve which is mounted
on the second cap and is selectively opened by pushing force of the piston to communicate
the second cushioning chamber with the second passages; a first quick fluid supply
valve which is mounted on the first cap and is selectively opened as pressurized pressure
flows into the first chamber to rapidly supply fluid to the second cushioning chamber;
and a second quick fluid supply valve which is mounted on the second cap and is selectively
opened as pressurized pressure flows into the second chambers to rapidly supply fluid
to the first cushioning chamber.
[0021] In another aspect, the present invention provides the pneumatic cylinder, wherein
each first and second cushioning sleeve comprises: a plurality of orifices through
which inner and outer portions of the cushioning sleeve communicate with each other;
a plurality of circumferential grooves formed on an inner circumference of the cushioning
sleeve and communicating with the orifices; and a plurality of longitudinal groove
formed along an longitudinal direction of the inner circumference of the cushioning
sleeve to communicate the circumferential grooves with each other.
[0022] In still another aspect, the present invention provides the pneumatic cylinder, wherein
the first and second fluid exhaust valves includes a valve body provided with a central
hole penetrating its central portion and communicating with the ports, a screw thread
formed on an outer circumference of the valve body and screw coupled to a screw thread
formed on an inner circumference of a valve hole formed on the first and second caps,
a poppet valve having a head portion located within the valve hole with a predetermined
gap and a stem portion penetrating the central hole with a predetermined gap.
[0023] It is to be understood that both the foregoing general description and th following
detailed description are exemplary and explanatory only and are not restrictive of
the invention, as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The accompanying drawings, which are incorporated in and constitute a part of this
specification, illustrate one embodiment of the invention and together with the description,
serve to explain the principles of the invention.
Fig. 1 is a sectional view illustrating a conventional pneumatic cylinder;
Fig. 2 is a sectional view illustrating an operation state of the pneumatic cylinder
depicted in Fig 1;
Fig. 3 is a sectional view illustrating a pneumatic cylinder in accordance with a
preferred embodiment of the present invention;
Fig. 4 is a sectional view illustrating an operation state of the pneumatic cylinder
depicted in Fig. 3;
Fig. 5 is a partial perspective view illustrating a cushioning sleeve of a pneumatic
cylinder in accordance with a preferred embodiment of the present invention;
Fig. 6 is a sectional view illustrating the cushioning sleeve depicted in Fig. 5;
Fig. 7 is a partial section, perspective view illustrating a quick fluid exhaust valve
of a pneumatic cylinder in accordance with a preferred embodiment of the present invention;
Fig. 8 is a sectional view illustrating the quick fluid exhaust valve depicted in
Fig. 8;
Fig. 9 is a partial section, perspective view illustrating a quick fluid supply valve
of a pneumatic cylinder in accordance with a preferred embodiment of the present invention;
Fig. 10 is a sectional view illustrating the quick fluid supply valve depicted in
Fig. 9; and
Fig. 11 is a graph for comparing a shock power change in response to cushioning operation
time and cushioning force of the piston between the cushioning device of the present
invention and the conventional cushioning device.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0025] Reference will now be made in detail to the present preferred embodiment of the invention,
an example of which is illustrated in the accompanying drawings. Wherever possible,
the same reference numbers will be used throughout the drawings to refer to the same
or like parts.
[0026] Certain terminology will be used in the following description for convenience and
reference only and will not be limiting. The words "right" and "left" will designate
directions in the drawings to which reference is made.
[0027] Referring to Figs. 3 and 4, the inventive pneumatic cylinder includes a barrel-like
cylindrical tube 2, a pair of caps 4 and 6 which are fixedly disposed on opposite
ends of the cylinder tube 2, respectively, and cushion regulator valves 8 and 10 for
regulating cushioning force which are mounted on the caps 4 and 6, respectively. The
caps 4 and 6 are respectively provided with fluid flow port 12 and 14 and fluid passages
24 and 26 communicating with the ports 12 and 14, respectively.
[0028] Further, a piston rod 18 slidably extends through the cap 4 into the inside of the
tube 102 and a piston 108 is fixed at one end of the rod 110 which is located in the
inside of the tube. Accordingly, the cylinder is to be provided with a first cushioning
chamber 28 which is defined by the right face of the cap 4 and the left face of the
piston with the inner circumference of the tube 2 and a second cushioning chamber
30 which is defined by the left face of the cap 6 and the right face of the piston
16 with the inner circumference of the tube 2.
[0029] The cylinder further includes a cushioning device for preventing shocks caused by
the piston 16 which reciprocates as fluid flows between each cushioning chamber 28
and 30 and a fluid tank(not shown). The cushioning device includes a first cushioning
sleeve 20 fixed around one end of the piston rod which is adjacent to the piston 16
and a second cushioning sleeve 22 fixed on the right face of piston 16 by means of
a bolt 31 and extending in a direction opposite to the piston rod 18. The cushioning
sleeves 20 and 22 have the same structure as each other. such that as the cushioning
sleeves 20 and 22 is inserted into respective passages 24 and 26 communicating with
the ports 12 and 14, respectively, communicating amount between each cushioning chamber
28 and 30 and each passages 24 and 26 is gradually reduced.
[0030] As shown in Figs, 5 and 6, the cushioning sleeve 20(22) is provided with a plurality
of orifices O through which inner and outer portion of each cushioning sleeve 20(22)
communicates with each other.
[0031] Further, the cushioning sleeve 20(22) is provided with a plurality of circumferential
grooves H formed on their inner circumference and a plurality of longitudinal groove
H' formed along its longitudinal direction and communicating the circumferential grooves
H with each other. Accordingly, the passages 24 and 26 are to communicate with each
cushioning chamber 28 and 30 through the orifices, the circumferential grooves, and
the longitudinal grooves O, H, and H'.
[0032] And, a V-shape packing 9 is fixed on each inner end of the passages 24 and 26 to
move the cushion sleeves while maintaining a predetermined gap between the cushioning
sleeve 20(22) and the passage 24(26)as well as providing a temporary fluid tight seal.
[0033] The cushioning device also includes quick fluid exhaust valves 32 and 34, having
the same structure as each other, which are mounted respectively on the caps 4 and
6. The quick fluid exhaust valve 32 is opened by being pressed by the left face of
the piston 16 when the piston 16 moves leftward, thereby selectively communicating
the cushioning chamber 28 and the passage 24 with each other. Further, the quick fluid
exhaust valve 34 is opened by being pressed by the right face of the piston when the
piston moves rightward, thereby selectively communicating the cushioning chamber 30
and the passage 26 with each other.
[0034] As shown in Figs. 7 and 8, the quick fluid exhaust valve 32(34) includes a valve
body 40 provided with a central hole 36 penetrating its central portion and communicating
with ports 12 and 14. Further, the valve body is provided with a screw thread 38 formed
on its outer circumference which is screw coupled to a screw thread 42 formed on the
inner circumference of the valve holes 48 and 50 formed on the caps 4 and 6, respectively.
[0035] The quick fluid exhaust valve 32(34) further includes a poppet valve 52 having a
head portion 44 located within each valve hole 48 and 50 with a predetermined gap
and a stem portion 56 penetrating the central hole 36 with a predetermined gap.
[0036] Since there is a predetermined gap between the inner circumfernce of the valve hole
48 and the head portion 44 of the poppet valve 52, the cushioning chambers 28 and
30 can selectively communicate with each port 12 and 14, respectively, in accordance
with open and close of the central hole 36 by the head portion 44.
[0037] The head portion 44 of the poppet valve 52 is biased by an elastic member 35 in the
valve hole 48 and 50 to maintain the close state of the central hole 36 before the
stem portion 56 is pushed by the piston 16.
[0038] The cushioning device further includes quick fluid supply valves 60 and 62, having
the same structure as each other, so that the fluid can be quickly fed to each cushioning
chamber 28 and 30 through each ort 12 and 14 by regulating the opening of each fluid
supply valve 60 and 62, thereby enabling the piston 16 to rapidly perform working
stroke.
[0039] Referring to Figs. 9 and 10, the quick fluid supply valve 60(62) includes a valve
body 68 provided with a fluid communication hole 72 penetrating its central portion
and communicating with port 12 and 14. Further, the valve body 68 is provided with
a screw thread 70 formed on its outer circumference which is screw coupled to a screw
thread 74 formed on the inner circumference of the valve hole 64 formed respectively
on the cap 4 and 6.
[0040] The valve hole 72 respectively communicates with the cushioning chambers 28 and 30
through the fluid communicating hole 72. Further, a check ball 76 is positioned in
the valve hole 64 and is biased by an elastic member 75' against the valve body 68
to selectively open and close the valve hole 64.
[0041] The check ball 76 opens the valve hole 64 in accordance with pressurized fluid fed
through the ports 12 and 14.
[0042] Referring to FIGS 3 and 4, reference mumeral 80 designates a wearing for reducing
friction resistance numeral 82 designtes an O-ring for sealing, reference 84 designates
a guarder ring for sealing, and numeral 86 designates a magnetic band for supplying
with position information necessary for stroke control of the piston 16 responding
to a movment of the piston 16.
[0043] The operation of the pneumatic cylinder as described above will be described hereinafter
in detail.
[0044] When pressurized pressure is supplied to the left cushioning chamber 28 through the
port 12, the piston with the piston rod 18 is forced to the right by the pressurized
fluid and thus fluid within the right cushioning chamber 30 exhausts to the fluid
tank (not shown) through the passage 26 via the port 14 formed on the cap 6.
[0045] At this point, when the piston moves to a cushioning operation range such that the
cushioning sleeve 22 mounted fixedly on the piston 16 is inserted into the passage
26 to close this passage 26, the piston is to receive cushioning force by fluid which
is temporarily stagnant within the right cushioning chamber 30.
[0046] And, the stagnant fluid within the right chamber 30 is compressed by the piston 16
as the pressurized fluid is continuously supplied to the left chamber 28 such that
the cushioning sleeve 22 is further inserted into the port 26. Accordingly, the cushioning
chamber 30 and the passage 14 is to be decreasingly gradually communicated with each
other through the orifices, circumference grooves, and the longitudinal grooves O,
H, and H' all of which are formed on the cushioning sleeve 22 to increasingly gradually
apply cushioning force to the piston 18.
[0047] Further, when the piston 16 pushes the stem portion 56 of the poppet valve 52 of
the quick fluid exhaust valve 34 as cushioning force is gradually decreasingly applied
to the piston, the poppet valve 54 overcomes elastic force of the elastic member 35
to move rightward itself such that the head portion 46 opens the central hole 38 of
the valve body 42, thereby communicating the cushioning chamber 30 with the fluid
passage port formed on the cap 6. As a result, the residual fluid within the chamber
22 returns to the fluid tank (not shown) to rapidly eliminate cushioning force applied
to the piston 16.
[0048] And then, when pressurized pressure is supplied to the right chamber 30 through the
port 14 via the passage 26 to accomplish the reciprocating motion of the piston rod
18, the piston 16 with the piston rod 18 is forced to the left by the pressurized
fluid and thus fluid within the left cushioning chamber 28 exhaust to the fluid tank
(not shown) through the port 12 via the passage 24 formed on the cap 4.
[0049] At this point, when the piston moves to a cushioning operation range such that the
cushioning sleeve 20 mounted fixedly around the piston rod 18 is inserted into the
passage 24 to close this passage 24, the piston is to receive cushioning force by
fluid which is temporally stagnant within the left cushioning chamber 28.
[0050] And, the stagnant fluid within the right chamber 30 is compressed by the piston 16
as the pressurized fluid is continuously supplied to the right chamber 30 such that
the cushioning sleeve 20 is further inserted into the passage 24. Accordingly, the
cushioning chamber 28 and the port 12 is to be decreasingly gradually communicated
with each other through the orifices, circumference grooves, and the longitudinal
grooves O, H, H' all of which are formed on the cushioning sleeve 20 to increasingly
gradually apply cushioning force to the piston 18.
[0051] Further, when the piston 16 pushes the stem portion 56 of the poppet valve 52 of
the quick fluid exhaust valve 32 as cushioning force is gradually decreasingly applied
to the piston, the poppet valve 54 overcomes elastic force of the elastic member 35
to move leftward itself such that the head portion 46 opens the central holes 38 of
the valve body 42, thereby communicating the cushioning chamber 28 with the port 12
formed on the cap 6. As a result, the residual fluid within the chamber 28 returns
to the fluid tank (not shown) to rapidly eliminate cushioning force applied to the
piston 16.
[0052] Fig. 11 is a graph for showing shock pressure characteristic with respect to the
stroke time of the piston according to the present invention.
[0053] The graph Y shows that the cushioning force is applied to the piston during a stroke
time of a section "Tsd" and the maximum shock pressure occurring at this section is
below 5 kg f/cm
2. This makes the piston rod 18 perform a rapid operation stroke since the time that
the cushioning force is applied to the piston is short, as compared with a time of
a graph X according to the prior art cylinder. Additionally, this makes the shock
pressure generated in the pneumatic cylinder decrease
[0054] Further, likewise the conventional art, the opening of the valve hole can be regulated
by the cushioning regulating valves 8 and 10, which makes it possible to control the
communication amount of fluid, thereby regulating the magnitude of the cushioning
force applied to the piston 16.
[0055] It will be apparent to those skilled in the art that various modifications and variations
can be made in the pneumatic cylinder of the present invention and in construction
of this system without departing from the scope or spirit of the invention.
[0056] Other embodiments of the invention will be apparent to those skilled in the art from
consideration of the specification and practice of the invention disclosed herein.
It is intended that the specification and examples be considered as exemplary only,
with a true scope and spirit of the invention being indicated by the following claims.
1. A pneumatic cylinder comprising:
a cylindrical tube;
first and second caps respectively fitted on opposite ends of the cylinder tube, said
first and second caps being provided with first and second fluid flowing ports, respectively;
first and second cushioning regulator valves respectively mounted on said first and
second caps to regulate cushioning force;
a piston rod slidably extending through one of the caps into the tube;
a piston fixed at one end of said piston rod which is located in the cylindrical tube;
and
a cushioning device for preventing shocks caused by said piston which reciprocates
when fluid flows in or out through the fluid flowing ports; wherein said cushioning
device comprises
a first cushioning sleeve fixed on the piston and extending in a direction opposite
to said piston rod, said first cushioning sleeve gradually decreasingly communicating
a first cushioning chamber with a first passage formed on the first cap and connected
to the first fluid flowing ports as said first cushioning sleeve is gradually inserted
into the first passage;
a second cushioning sleeve fixed around the one end of said piston rod, said second
cushion sleeve gradually decreasingly communicating a second cushioning chamber with
a second passage formed on the second caps and connected to the second fluid flowing
ports as said second cushioning sleeve is gradually inserted into the second passage;
a first quick fluid exhaust valve which is mounted on the first cap and is selectively
opened by pushing force of said piston to communicate the first cushioning chamber
with the first passage;
a second quick fluid exhaust valve which is mounted on the second cap and is selectively
opened by pushing force of said piston to communicate the second cushioning chamber
with the second passages;
a first quick fluid supply valve which is mounted on the first cap and is selectively
opened as pressurized pressure flows into the first chamber to rapidly supply fluid
to the second cushioning chamber; and
a second quick fluid supply valve which is mounted on the second cap and is selectively
opened as pressurized pressure flows into the second chambers to rapidly supply fluid
to the first cushioning chamber.
2. The pneumatic cylinder as claimed in claim 1, wherein each first and second cushioning
sleeve comprises:
a plurality of orifices through which inner and outer portions of said cushioning
sleeve communicate with each other;
a plurality of circumferential grooves formed on an inner circumference of said cushioning
sleeve and communicating with the orifices; and
a plurality of longitudinal groove formed along an longitudinal direction of the inner
circumference of said cushioning sleeve to communicate the circumferential grooves
with each other.
3. The pneumatic cylinder as claimed in claim 1, wherein each of said first and second
fluid exhaust valves includes a valve body provided with a central hole penetrating
its central portion and communicating with the ports, a screw thread formed on an
outer circumference of the valve body and screw coupled to a screw thread formed on
an inner circumference of a valve hole formed on the first and second caps, a poppet
valve having a head portion located within the valve hole with a predetermined gap
and a stem portion penetrating the central hole with a predetermined gap, and an elastic
member inserted between the valve hole and the head portion of the poppet valve for
urging the poppet valve in the direction of the cushing chamber.
4. The pneumatic cylinder as claimed in claim 1, wherein each of said first and second
quick fluid supply valves includes a valve body provided with a fluid communication
hole penetrating its central portion and communicating with passages, a screw thread
formed on an outer circumference of the valve body and screw coupled to a screw thread
formed on an inner circumference of a valve hole formed on the first and second caps,
and a check ball positioned in the valve hole and biased by an elastic member against
the valve body to selectively open and close the valve hole.